Semiconductor integrated circuit device and power supply voltage monitor system employing it

Abstract

A semiconductor integrated circuit device, i.e. a reset IC( 1 ), includes: a detection circuit ( 4 ) for detecting whether an input voltage (Vin) has risen or dropped by comparing the input voltage (Vin) with a reference voltage; a delay circuit ( 8 ) for delaying a start-up voltage detection signal from the detection circuit ( 4 ) by charging a capacitor (C) connected thereto via a connection terminal (CT), and discharging the capacitor (C) by receiving an output signal (Vout) of a first voltage; a retention circuit ( 9 ) for retaining a start-up voltage detection signal delayed by the delay circuit ( 8 ); and a driver ( 10 ) for generating an output signal (Vout) that becomes a first voltage by a start-up voltage detection signal retained by the retention circuit ( 9 ), and generating an output signal (Vout) that becomes a second voltage by a voltage drop detection signal from the detection circuit ( 4 ).

1. A semiconductor integrated circuit device that monitors an input voltage by comparing the input voltage with a predetermined voltage, and outputs a voltage representing a result of comparison, the semiconductor integrated circuit device comprising:
 a detection circuit to detect that the input voltage has risen by comparing the input voltage with a reference voltage, and to output a detection signal of the input voltage; 
 a delay circuit to delay the detection signal from the detection circuit by a time constant adjustment method; 
 a connection terminal to which a capacitor is connected; 
 a retention circuit to receive an output of the detection circuit and an output of the delay circuit, and to retain the detection signal delayed by the delay circuit, and 
 a driver to generate a first voltage according to the detection signal retained by the retention circuit and to inhibit an output of the detection signal immediately when the detection circuit detects that the input voltage has dropped, 
 wherein the delay circuit is arranged to delay the detection signal from the detection circuit by charging the capacitor via the connection terminal, and to discharge the capacitor by outputting the detection signal, 
 wherein the delay circuit includes:
 a charging resistance connected between a direct-current power supply and the connection terminal, 
 a first switch connected between the connection terminal and ground, 
 a logic gate to turn off the first switch when the detection signal from the detection circuit and the monitor signal of a second voltage are fed thereto, and 
 an amplifier to output a high level or low level signal according to a voltage of the connection terminal, 
 
 wherein the semiconductor integrated circuit device is arranged to provide, as an output monitor signal, a voltage generated by the driver. 
 
   
   
     2. The semiconductor integrated circuit device of  claim 1 ,
 wherein the delay circuit includes a second switch connected between the direct-current power supply and the charging resistance, the second switch operable to perform a reverse on/off operation of the first switch. 
 
   
   
     3. The semiconductor integrated circuit device of  claim 1 ,
 wherein the retention circuit is a D latch that is set when the detection signal delayed by the delay circuit is fed thereto as a clock input, and is reset when the detection circuit detects that the input voltage has dropped. 
 
   
   
     4. The semiconductor integrated circuit device of  claim 1 ,
 wherein the retention circuit is a switch circuit that connects and disconnects the delay circuit to and from the driver according to an output of the detection circuit and the monitor signal. 
 
   
   
     5. The semiconductor integrated circuit device of  claim 4 ,
 wherein the switch circuit comprises a third switch that turns on when the monitor signal is the first voltage and a fourth switch that turns on when the detection signal from the detection circuit is fed thereto, the third and fourth switches being connected in parallel between the delay circuit and the driver. 
 
   
   
     6. A power supply voltage monitor system comprising:
 the semiconductor integrated circuit device of  claim 1 ; 
 wherein the power supply voltage monitor system causes the semiconductor integrated circuit device to: 
 monitor a power supply voltage to be fed to an electronic appliance, and 
 switch a control portion of the electronic appliance between a reset state and a non-reset state according to the monitor signal from the semiconductor integrated circuit device. 
 
   
   
     7. A power supply voltage monitor system comprising:
 the semiconductor integrated circuit device of  claim 3 ; 
 wherein the power supply voltage monitor system causes the semiconductor integrated circuit device to:
 monitor a power supply voltage to be fed to an electronic appliance, and 
 switch a control portion of the electronic appliance between a reset state and a non-reset state according to the monitor signal from the semiconductor integrated circuit device. 
 
 
   
   
     8. A power supply voltage monitor system comprising:
 the semiconductor integrated circuit device of  claim 4 ; 
 wherein the power supply voltage monitor system causes the semiconductor integrated circuit device to:
 monitor a power supply voltage to be fed to an electronic appliance, and 
 switch a control portion of the electronic appliance between a reset state and a non-reset state according to the monitor signal from the semiconductor integrated circuit device. 
 
 
   
   
     9. A power supply voltage monitor system comprising:
 the semiconductor integrated circuit device of  claim 5 ; and 
 wherein the power supply voltage monitor system causes the semiconductor integrated circuit device to:
 monitor a power supply voltage to be fed to an electronic appliance, and 
 switch a control portion of the electronic appliance between a reset state and a non-reset state according to the monitor signal from the semiconductor integrated circuit device.